Lung cancer is the leading cause of cancer deaths in the U.S. Many pulmonary carcinomas are detected as nodules in asymptomatic patients at a time when curative resection is most likely. Several studies have shown that dual-energy radiography, with its separate display of bone and soft tissue information, improves the detection of pulmonary nodules over that of the conventional film. In addition, dual-energy imaging is able to characterize nodules as benign or potentially malignant based on its ability to detection calcium within the nodule. Systems investigated to date have included a fan beam with an energy sensitive detector and conventional x-ray exposure of a dual-energy phosphor plate system. The former was limited by poor beam utilization while the latter approaches have suffered from lack of adequate scatter control and overly simplistic calibration methodologies. We propose to construct and to investigate a scatter-free dual-energy chest radiography unit with the following characteristics: (1) A scanning slit system using a 1 cm wide beam that provides adequate beam utilization and eliminates scatter. (2) An energy-sensitive detector consisting of 3 BaFBr storage phosphor plates with additional copper filtration between the initial and second plates, creating adequate low and high energy image photon fluences and energy separation. (3) Image processing optimization including methods to accurately calibrate large area energy sensitive detectors, accurately register multiple plates and correct for small differences in plate magnification, and noise reduction algorithms. The proposed research provides for excellent scatter control which has been a major obstacle in development of high-quality dual-energy images using phosphor plate technology. Protocols are proposed dealing with detectability and characterization of pulmonary nodules in phantom models and clinical situations and in detection and evaluation of major airway disease. It is anticipated that the proposed research will demonstrate the clinical benefit that can be realized from a practical and cost-effective approach to dual-energy chest radiography.